nx_framed_append.nx

nx_framed_append.nx -- WMS-R0: the ATOMIC FRAMED-APPEND collision floor. module: nishi-core.storage.framed_append capability: CORE_COMPUTE (a reusable durability primitive) ROOT CAUSE this closes: status channels (e.g. nx_conductor_notes.nx) emit ONE log record as a SEQUENCE of separate sys_write() calls ("NOTES epoch=" then the number then " weakest_arc=" ...). O_APPEND only makes a SINGLE write() atomic, NOT a sequence -- so two concurrent appenders interleave between those writes and the file gets a TORN line ("NOTES epoch=NOTES epoch=..."). There was no framing primitive anywhere in the substrate. THE FIX (one capability): build the WHOLE record into ONE buffer, terminate it with a single '\n', and emit EXACTLY ONE sys_write() to an O_APPEND fd. Under O_APPEND that single write is atomic by the kernel's guarantee -> concurrent appenders can never interleave -> ZERO torn lines. Length is BOUNDED (cap): an oversized record is REJECTED (-2), never silently truncated or torn. REUSE / lineage: the "one buffer -> one write" discipline + decimal/string buffer assembly are lifted directly from nx_seg_store.nx (ss_writefile single write loop; ss_cat / ss_catn buffer builders). Sovereign: only nx_syscalls. Other organs CALL fa_append/fa_appendz -- a follow-up rung rewrites nx_conductor_notes's multi-write block to a single fa_appendz call. license_tier: ORIGINAL